1. Field of the Invention
The present invention relates to a quartz optical waveguide which has a function such as laser amplification or a nonlinear optical effect and a method for producing such functional quartz optical waveguide.
2. Description of the Related Art
Among optical waveguides, a quartz optical waveguide comprising quartz glass attracts attentions since it has a low light transmission loss and can be connected with a quartz optical fiber with a low connection loss.
In general, such quartz optical waveguide is produced by a combined method of glass film formation by a flame hydrolysis deposition (FHD) and fine processing of the formed glass film by reactive ion etching (RIE) (cf. Masao Kawachi, "Quartz Optical Waveguides and Their Application in Integrated Optical Elements", OPTICS, 18 (12), December 1989, 681-686).
The above method for producing a quartz optical waveguide will be explained by making reference to FIG. 1.
As shown in FIG. 1A, a glass-forming raw material such as SiCl.sub.4, TiCl.sub.4 and the like are supplied to a burner 1 together with a fuel gas (e.g. hydrogen gas, oxygen gas, etc.) and hydrolyzed and oxidized in an oxyhydrogen flame 2 to form fine particles 3 (soot) of glass. The glass soot is then deposited on a support 4 such as a silicon wafer to successively form films of glass soot 5a and 5b which have different compositions from each other. The deposited glass films on the support 4 are vitrified by heating them at a high temperature to obtain a buffering layer 6a and a core layer 6b as shown in FIG. 1B.
The above method is FHD.
Then, by RIE, unnecessary parts of the core layer 6b are removed to remain a ridge-form core part 6c as shown in FIG. 1C. Again, by FHD, a cladding layer 6d is formed to surround the core part 6c to form an embedded type quartz optical waveguide 7 as shown in FIG. 1D.
Since the above described FHD makes it possible to produce a quartz film having a low light transmission loss at a high film forming rate, it is most widely used in the production of the quartz optical waveguide. However, most of the optical waveguides produced by this method are used as passive type optical elements such as an element for merging and dividing light or an element for branching.
Then, it is highly desired to provide a functional optical waveguide which has a function such as laser amplification or a switching function using a nonlinear optical effect.
To realize such function, it is necessary to add a rare earth element which has a laser generating function or semiconductor fine particles which have a nonlinear optical effect to the optical waveguide. However, it is difficult to synthesize a glass containing the rare earth element or the semiconductor material which is unstable at high temperature, since FHD synthesizes the glass in an oxyhydrogen flame having a temperature of 2000.degree. C. or higher.